U.S. patent application number 13/893248 was filed with the patent office on 2014-11-13 for thermally stable low random telegraph noise sensor.
This patent application is currently assigned to HGST Netherlands B.V.. The applicant listed for this patent is HGST NETHERLANDS B.V.. Invention is credited to Koujiro Komagaki, Kouichi Nishioka.
Application Number | 20140334031 13/893248 |
Document ID | / |
Family ID | 51864601 |
Filed Date | 2014-11-13 |
United States Patent
Application |
20140334031 |
Kind Code |
A1 |
Nishioka; Kouichi ; et
al. |
November 13, 2014 |
THERMALLY STABLE LOW RANDOM TELEGRAPH NOISE SENSOR
Abstract
In one embodiment, magnetic read head includes a seed layer
including an amorphous alloy film and Ru film positioned thereon,
and an antiferromagnetic (AFM) layer positioned above the seed
layer, the AFM layer including an alloy of MnIr having an L.sub.12
ordered phase, the amorphous alloy including a Co--X alloy having
more Co than any other element, with X including at least one of:
Zr, Nb, Ta, Hf, W, Si, and Al. In another embodiment, a method for
forming a magnetic read head includes forming a seed layer above a
substrate, heating at least the substrate to a first temperature in
a range from about 150.degree. C. to about 300.degree. C., cooling
at least the substrate to a second temperature of less than about
100.degree. C., and forming an AFM layer above the seed layer
between the heating and the cooling, the AFM layer comprising a
MnIr alloy.
Inventors: |
Nishioka; Kouichi;
(Hiratsuka-shi, JP) ; Komagaki; Koujiro;
(Odawara-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HGST NETHERLANDS B.V. |
Amsterdam |
|
NL |
|
|
Assignee: |
HGST Netherlands B.V.
Amsterdam
NL
|
Family ID: |
51864601 |
Appl. No.: |
13/893248 |
Filed: |
May 13, 2013 |
Current U.S.
Class: |
360/75 ; 427/129;
428/812 |
Current CPC
Class: |
G11B 5/3906 20130101;
G11B 5/3163 20130101; Y10T 428/115 20150115; H01L 43/08
20130101 |
Class at
Publication: |
360/75 ; 428/812;
427/129 |
International
Class: |
G11B 21/02 20060101
G11B021/02 |
Claims
1. A magnetic read head, comprising: an antiferromagnetic (AFM)
layer comprising a MnIr alloy having an L.sub.12 ordered phase,
wherein a percentage of a volume of MnIr crystal grains in the MnIr
alloy having a magnetic relaxation time of about 1 msec or less
with respect to a total volume of MnIr is less than about 3% at a
maximum temperature of the magnetic read head during operation.
2. The magnetic read head as recited in claim 1, further
comprising: a seed layer positioned below the AFM layer; a pinned
layer positioned above the AFM layer; a barrier layer positioned
above the pinned layer, the barrier layer comprising MgO; and a
ferromagnetic free layer positioned above the barrier layer, the
ferromagnetic free layer being adapted to respond to an external
magnetic field, wherein a magnetic moment of the pinned layer is
strongly pinned by the AFM layer.
3. The magnetic read head as recited in claim 2, wherein the pinned
layer comprises: a first ferromagnetic layer (AP1) positioned above
the AFM layer; an exchange layer positioned above the first
ferromagnetic, layer; and a second ferromagnetic layer (AP2)
positioned above the exchange layer, wherein the exchange layer
comprises substantially pure Ru, wherein the AFM layer is strongly
magnetically coupled by exchange coupling with the first
ferromagnetic layer, and wherein the second ferromagnetic layer is
strongly antiparallel coupled with the first ferromagnetic
layer.
4. The magnetic read head as recited in claim 1, wherein the
percentage of the volume of the MnIr crystal grains in the MnIr
alloy having a magnetic, relaxation time of about 1 msec or less
with respect to the total volume of MnIr is less than about 1% at
the maximum temperature of the magnetic read head during
operation.
5. A system, comprising: a magnetic storage medium; at least one
magnetic read head as recited in claim 1 for reading from the
magnetic storage medium; and a control unit coupled to the magnetic
read head for controlling operation of the magnetic read head.
6. A magnetic read head, comprising: an antiferromagnetic (AFM)
layer comprising a MnIr alloy having an L.sub.12 ordered phase,
wherein less than about 3% of polycrystalline grains forming the
AFM layer have a crystal grain volume of about 1.2.times.10.sup.-19
cm.sup.3 or less.
7. The magnetic read head as recited in claim 6, further
comprising: a seed layer positioned below the AFM layer; a pinned
layer positioned above the AFM layer; a barrier layer positioned
above the pinned layer, the barrier layer comprising MgO; and a
ferromagnetic free layer positioned above the barrier layer, the
ferromagnetic free lave being adapted to respond to an external
magnetic field, wherein a magnetic moment of the pinned layer is
strongly pinned by the AFM layer.
8. The magnetic read head as recited in claim 7, wherein the pinned
layer comprises: a first ferromagnetic layer (AP1) positioned above
the AFM layer; an exchange layer positioned above the first
ferromagnetic layer; and a second ferromagnetic layer (AP2)
positioned above the exchange layer, wherein the exchange layer
comprises substantially pure Ru, wherein the AFM layer is strongly
magnetically coupled by exchange coupling with the first
ferromagnetic layer, and wherein the second ferromagnetic layer is
strongly antiparallel coupled with the first ferromagnetic
layer.
9. The magnetic read head as recited in claim 6, wherein less than
about 1% of polycrystalline grains forming the AFM layer have a
crystal grain volume of about 1.2=10.sup.-19 cm.sup.3 or less.
10. A system, comprising: a magnetic storage medium; at least one
magnetic read had as recited in claim 6 for reading from the
magnetic storage medium; and a control unit coupled to the magnetic
read head for controlling operation of the magnetic read head.
11. A magnetic read head, comprising: a seed layer comprising an
amorphous alloy film and a Ru film positioned thereon, and an
antiferromagnetic (AFM) layer positioned above the seed layer, the
AFM layer comprising an alloy of MnIr having an L.sub.12 ordered
phase, wherein the amorphous alloy comprises a Co--X alloy having
more Co than any other element, wherein X comprises at least one
of: Zr, Nb, Ta, Hf, W, Si, and Al.
12. The magnetic read head as recited in claim 11, wherein a
percentage of a volume of MnIr crystal grains in the MnIr alloy
having a magnetic relaxation time of about 1 msec or less with
respect to a total volume of MnIr is less than about 3% at as
maximum temperature of the magnetic read head during operation.
13. The magnetic read head as recited in claim 11, wherein less
than about 3% of polycrystalline grains forming the AFM layer have
a crystal grain volume of about 1.2=10.sup.-19 cm.sup.3 or
less.
14. The magnetic read head as recited in claim 11, further
comprising: a pinned layer positioned above the AFM layer; a
barrier layer positioned above the pinned layer, wherein the
barrier layer comprises MgO; and a ferromagnetic free layer
positioned above the barrier layer, the ferromagnetic free layer
being adapted to respond to an external magnetic field, wherein a
magnetic moment of the pinned layer is strongly pinned by the AFM
layer.
15. The magnetic read head as recited in claim 14, wherein the
pinned layer comprises: a first ferromagnetic layer (AP1)
positioned above the AFM layer; an exchange layer positioned above
the first ferromagnetic layer; and a second ferromagnetic layer
(AP2) positioned above the exchange layer, wherein the exchange
layer comprises substantially pure Ru, wherein the AFM layer is
strongly magnetically coupled by exchange coupling with the first
ferromagnetic layer, and wherein the second ferromagnetic layer is
strongly antiparallel coupled with the first ferromagnetic
layer.
16. A system, comprising: a magnetic storage medium; at least one
magnetic read head as recited in claim 11 for reading, from the
magnetic medium; and a control unit coupled to the magnetic read
head for controlling operation of the magnetic read head.
17. A method for forming a magnetic read head, the method
comprising: forming a seed layer above a substrate, the seed layer
comprising an amorphous alloy film of Co--X alloy and a Ru film
thereon, wherein the Co--X alloy includes more Co than any other
element, wherein X comprises at least one of: Zr, Nb, Ta, Hf, Si,
and Al; heating at least the substrate to a first temperature in a
range from about 150.degree. C. to about 300.degree. C.; forming an
antiferromagnetic (AFM) layer above the seed layer after the
heating, the AFM layer comprising a MnIr alloy; and cooling at
least the substrate to a second temperature of less than about
100.degree. C.
18. The method as recited in claim 17, further comprising: forming
a first ferromagnetic layer (AP1) above the AFM layer; forming an
exchange layer above the first ferromagnetic layer; forming a
second ferromagnetic layer (AP2) above the exchange layer, wherein
the first ferromagnetic layer, the exchange layer, and the second
ferromagnetic, layer form a pinned layer; forming a barrier layer
above the pinned layer; and forming a ferromagnetic free layer
above the barrier layer, the ferromagnetic free layer being adapted
to respond to an external magnetic field, wherein a magnetic moment
of the pinned layer is strongly pinned by the AFM layer, wherein
the AFM layer is strongly magnetically coupled by exchange coupling
with the first ferromagnetic layer, wherein the second
ferromagnetic layer is strongly antiparallel coupled with the first
ferromagnetic layer, and wherein the barrier layer comprises
MgO.
19. The method as recited in claim 17, wherein the MnIr alloy has
an L.sub.12 ordered phase, and wherein a percentage of a volume of
MnIr crystal grains in the MnIr alloy having a magnetic relaxation
time of about 1 msec or less with respect to a total volume of MnIr
is less than about 3% at a maximum temperature of the magnetic read
head during operation.
20. The method as recited in claim 17, wherein the MnIr alloy has
an L.sub.12 ordered phase, and wherein less than about 3% of
polycrystalline grains forming the AFM layer have a crystal grain
volume of about 1.2.times.10.sup.-19 cm.sup.3 or less.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to magnetic data storage and
retrieval, and more specifically, this invention relates to a
magnetic read head having a thermally stable low random telegraph
noise sensor and systems thereof.
BACKGROUND
[0002] In order to produce high recording densities in hard disk
drives (HDDs) recording bit length and recording track width of a
recording medium may be reduced, in one approach. In order to read
data from the recording medium having the recording bits with the
reduced track width, without substantial amounts of error, a track
width of a read head sensor (referred to as "read head track
width") and a stripe height (a depth from an air hearing surface of
the read head) may also be reduced. The track width and the stripe
height of the read head may be approximately 15 nm at a recording,
density of 2 terabytes per square inch (Tbpsi) and approximately 5
nm at a recording density of 5 Tbpsi.
[0003] The miniaturization of the read head sensor leads to a
smaller volume of the magnetic body from which the read sensor is
constructed. As a result, read noise is very undesirably large due
to the increased magnetic instability caused by the demagnetization
field of the magnetic body. In addition, miniaturization of the
sensor reduces sensor sensitivity. Therefore, problems relating to
degradation of the signal-to-noise ratio (SNR) and a significant
increase in the error rate are also observable. The magnetic bodies
forming the read sensor film may comprise an antiferromagnetic
layer, a pinned layer, and a free layer. Improvements in the
magnetic stability of these magnetic bodies would be very
beneficial to magnetic head manufacturing and usage.
[0004] The sensor changes resistance by using a tunneling effect of
electrons in an insulated barrier layer, which is referred to as
tunneling magnetic resistance (TMR). The sensor film may comprise a
seed layer, an antiferromagnetic layer on the seed layer, a pinned
layer formed on the antiferromagnetic layer, an insulated barrier
layer formed on the pinned layer, a free layer formed on the
insulated barrier layer, and a cap layer formed on the free
layer.
[0005] Using this construction, low-frequency noise below about 50
MHz has been observed. The low frequency noise appears to be
generated by the sensor, but attempts to reduce this noise, and to
guarantee the reliability of a hard disk drive (HDD) employing such
a sensor, have been unsuccessful.
[0006] A magnetic moment of the pinned layer is pinned by an
exchange coupling, force from the antiferromagnetic layer.
Conventionally, a MnIr disordered film having atoms arranged
randomly in the antiferromagnetic layer may be used. The
miniaturization of the stripe height accompanying the
miniaturization of the read head increases the demagnetization
field of the pinned layer, and the pinned layer becomes unstable;
therefore, sensor miniaturization and a stronger exchange coupling
force become necessary.
[0007] A large increase in the exchange coupling force between the
antiferromagnetic layer and the ferromagnetic layer of a L.sub.12
ordered alloy of Mn.sub.3Ir has been shown. K. Imakita et al.,
"Giant exchange anisotropy observed in Mn--Ir/Co--Fe bilayers
containing, ordered Mn.sub.3Ir phase," Appl. Phys. Lett., 85, 3812
(2004). L.sub.12 ordered Mn.sub.3Ir is an alloy of Mn and Ir with
an ordered placement of atoms that has a structure that places Mn
in the center positions of the faces in a face-centered cubic (fcc)
lattice and places Ir in the corner positions. When a sputtering
device is used to deposit film of MnIr at room temperature, a MnIr
disordered film is obtained. When growing an L.sub.12 ordered alloy
of MnIr, it has been reported that substrate heating, high gas
pressure film deposition, and cold film deposition processes are
required.
[0008] A film deposition chamber capable of high-temperature film
deposition and a cooling chamber capable of cooling the substrate
during the film deposition process, therefore, may be used to
deposit the ordered film of Mn.sub.3Ir. The fabrication of an
ordered alloy by hot film deposition has been attempted, and the
fabrication of a L.sub.12 ordered alloy of Mn.sub.3Ir was
confirmed. The results of X-ray diffraction measurements confirmed
a degree of order representing the extent of the ordered degree
from 0.15 to 0.30, and a substantial increase in the value of the
exchange coupling constant, Jk, that represents the strength of the
exchange coupling force between the antiferromagnetic layer and the
pinned layer from the conventional 0.6 erg/cm.sup.2 to 1.0
erg/cm.sup.2. Simultaneously, the blocking temperature, Tb, which
is the temperature characteristic, substantially increased from
250.degree. C. to 320.degree. C.
[0009] The film thickness of the antiferromagnetic layer was
thinned from 60 .ANG. to 40 .ANG. and used to fabricate a prototype
head because Jk and Tb were greatly enhanced by producing, a
L.sub.12 ordered alloy of Mn.sub.3Ir. The results were that the
exchange coupling constant Jk increased from 0.6 erg/cm.sup.2 to
0.9 erg/cm.sup.2, and the blocking temperature Tb was the same as
the conventional 250.degree. C.
[0010] In contrast to a conventional read head, and in spite of the
large increase in Jk, the prototype read head exhibited the
baseline variations in the read signal waveform and experienced
instability of the read waveform. The baseline variations in the
read signal waveform are referred to as random telegraph noise
(RTN) and are randomly generated over time. A prototype read head
having a thick antiferromagnetic layer was studied, and a
correlation between the generation of RTN and the antiferromagnetic
layer film thickness was confirmed. Therefore, it would be
beneficial to reduce the RTN which causes read errors.
SUMMARY
[0011] In one embodiment, a magnetic read head includes an
antiferromagnetic (AFM) layer comprising a MnIr alloy having an
L.sub.12 ordered phase, wherein a percentage of a volume of MnIr
crystal grains in the MnIr alloy having a magnetic relaxation time
of about 1 millisecond (msec) or less with respect to a total
volume of MnIr is less than about 3% at a maximum temperature of
the magnetic read head during operation.
[0012] In another embodiment, a magnetic read head includes an AFM
layer having a MnIr alloy having an L.sub.12 ordered phase, wherein
less than about 3% of polycrystalline grains forming the AFM layer
have a crystal grain volume of about 1.2.times.10.sup.-19 cm.sup.3
or less.
[0013] According to another embodiment, a magnetic read head
includes a seed layer having an amorphous alloy film and as Ru film
positioned thereon, along with an AFM layer positioned above the
seed layer, the AFM layer including an alloy of MnIr having an
L.sub.12 ordered phase, wherein the amorphous alloy includes a
Co--X alloy having more Co than any other element, wherein X
includes at least one of: Zr, Nb, Ta, Hf, W, Si, and Al.
[0014] In yet another embodiment, a method for forming a magnetic
read head includes forming a seed layer above a substrate, the seed
layer having an amorphous alloy film of Co--X alloy below a Ru
film, wherein the Co--X alloy includes more Co than any other
element, wherein X includes at least one of: Zr, Nb, Ta, Hf, W, Si,
and Al; heating at least the substrate to a first temperature in a
range from about 150.degree. C. to about 300.degree. C.; cooling at
least the substrate to a second temperature of less than about
100.degree. C.; and forming an AFM layer above the seed layer
between the hating and the cooling, the AFM layer including a MnIr
alloy.
[0015] Any of these embodiments may be implemented in a magnetic
data storage system such as a disk drive system, which may include
a magnetic head, a drive mechanism for passing a magnetic storage
medium (e.g., hard disk) over the head, and a control unit
electrically coupled to the head for controlling operation of the
head.
[0016] Other aspects and advantages of the present invention will
become apparent from the following detailed description, which,
when taken in conjunction with the drawings, illustrate by way of
example the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1A is a schematic diagram of a laminated structure of a
TMR sensor.
[0018] FIG. 1B shows a table for materials and structures in
various exemplary laminated structures of a TMR sensor.
[0019] FIG. 2A shows a diagram of a face-centered cubic (fcc)
crystal of MnIr.
[0020] FIG. 2B shows a crystal structure of L.sub.12 MnIr.
[0021] FIG. 3 shows the degree of order of the L.sub.12 structure
of each sensor film A, B, and E.
[0022] FIG. 4 shows analysis of MnIr crystal grain sizes for each
sensor film A, B, and E.
[0023] FIG. 5 shows temperature dependence of magnetocrystalline
anisotropic constant Ka of MnIr for each sensor film A, B, and
E.
[0024] FIG. 6 shows the frequency dependence of the MnIr population
with the magnetic fluctuation frequency (f) for each sensor film A,
B, and E.
[0025] FIG. 7 shows the MnIr component of magnetic fluctuations
within time .tau. for each sensor film A, B, and E.
[0026] FIG. 8 shows the relationship between MnIr crystal grain
size and magnetic relaxation time .tau. for sensor film E.
[0027] FIG. 9 shows the relationship between MnIr crystal grain
volume and magnetic relaxation time .tau. for sensor film E.
[0028] FIG. 10A shows empirical results and calculation results of
exchange coupling magnetic field Hp of MnIr and AP1 and the
temperature changes of the coercive force for sensor film A.
[0029] FIG. 10B shows empirical results and calculation results of
exchange coupling magnetic field Hp of MnIr and AP1 and the
temperature changes of the coercive force for sensor film B.
[0030] FIG. 10C shows empirical results and calculation results of
exchange coupling magnetic field Hp of MnIr and AP1 and the
temperature changes of the coercive force for sensor film E.
[0031] FIG. 11 is a simplified drawing, of a magnetic recording,
disk drive system.
[0032] FIG. 12 is a flowchart of a method in accordance with one
embodiment.
DETAILED DESCRIPTION
[0033] The following description is made for the purpose of
illustrating the general principles of the present invention and is
not meant to limit the inventive concepts claimed herein. Further,
particular features described herein can be used in combination
with other described features in each of the various possible
combinations and permutations.
[0034] Unless otherwise specifically defined herein, all terms are
to be given their broadest possible interpretation including
meanings implied from the specification as well as meanings
understood by those skilled in the art and/or as defined in
dictionaries, treatises, etc.
[0035] It must also be noted that, as used in the specification and
the appended claims, the singular forms "a," "an" and "the" include
plural referents unless otherwise specified.
[0036] In one general embodiment, a magnetic read head includes an
antiferromagnetic (AFM) layer comprising a MnIr alloy having an
L.sub.12 ordered phase, wherein a percentage of a volume of MnIr
crystal grains in the MnIr alloy having a magnetic relaxation time
of about 1 millisecond (msec) or less with respect to a total
volume of MnIr is less than about 3% at a maximum temperature of
the magnetic read head during operation.
[0037] In another general embodiment, a magnetic read head includes
an AFM layer having a MnIr alloy having an L.sub.12 ordered phase,
wherein less than about 3% of polycrystalline grains forming the
AFM layer have a crystal grain volume of about 1.2.times.10.sup.-19
cm.sup.3 or less.
[0038] According to another general embodiment, a magnetic read
head includes a seed layer having an amorphous alloy film and a Ru
film thereon, along with an AFM layer positioned above the seed
layer, the AFM layer including an alloy of MnIr having an L.sub.12
ordered phase, wherein the amorphous alloy includes more Co than
any other element in a Co--X alloy, wherein X includes at least one
of: Zr, Nb, Ta, Hf, W, Si, and Al.
[0039] In yet another general embodiment, a method for forming a
magnetic read head includes forming a seed layer above a substrate,
the seed layer including an amorphous alloy film positioned below a
Ru film, wherein the amorphous alloy includes a Co--X alloy having
more Co than any other element, wherein X includes at least one of:
Zr, Nb, Ta, Hf, W, Si, and Al; heating, at least the substrate to a
first temperature in a range from about 150.degree. C. to about
300.degree. C.; cooling at least the substrate to a second
temperature of less than about 100.degree. C.; and forming an AFM
layer above the seed layer between the heating and the cooling, the
AFM layer including a MnIr alloy.
[0040] Focusing on the AFM layer adjacent to the pinned layer of a
read head, the time and temperature characteristics of thermal
magnetic fluctuations were examined. When the volume percentage of
AFM crystal grains having frequencies of the fluctuations is
plotted with respect to the frequency of the magnetic thermal
fluctuations of the AFM crystal, as the frequency of the
fluctuations decreased, the number of AFM layer crystal grains
increases (for more details, see FIG. 6). In other words, there is
a large number of AFM crystals that have a low frequency and slow
fluctuations. This kind of frequency dependence is referred to as
1/f noise. There are almost no components having high-frequency
fluctuations particularly above the frequency of 50 MHz. In the
frequency band below 50 MHz, the number of AFM crystal grains
increases rapidly with the decrease in frequency.
[0041] This tendency is identical to the frequency characteristics
of random telegraph noise, which is the main noise of a read head.
Thus, it is clear that the main source of read head noise is the
magnetic fluctuations of the AFM crystals.
[0042] The noise that negatively affects the read process of the
read head is random telegraph noise having frequencies of at least
1 kHz. At frequencies below 1 kHz, the probability of interfering
with the signal read is low because the generation frequency is
small with respect to the frequency of the read signal, in one
approach.
[0043] Thus, to suppress noise that negatively affects the signal
read process, the AFM crystal grains having magnetic fluctuations
at frequencies above 1 kHz are reduced.
[0044] According, to one embodiment, the AFM layer may comprise a
MnIr alloy having the L.sub.12 ordered phase in one approach, of
the polycrystalline grains forming the AFM layer, the total volume
of the crystal grains (crystal nanograms) having a crystal gram
volume of less than or equal to about 1.2.times.10.sup.-19 cm.sup.3
may be about 3%, and preferably about 1% and less, than a volume of
the entire AFM layer (derived while considering the correlation of
the magnetic anisotropic energy of the crystal grains and the
frequency).
[0045] In another embodiment, a volume ratio of the MnIr crystal
grains having a magnetic relaxation time .tau.(=1/f) of about 1
msec or shorter with respect to the total volume of MnIr may be no
more than about 3%, and preferably about 1%, at a maximum
temperature of the read head in practical applications such as
during operation of the read head to read data from a magnetic
medium for a period to time. The maximum temperature may be
determined easily via experimentation, by passing the sense current
therethrough until a steady state temperature is achieved and
measuring the temperature, and preferably in an environment similar
to that of actual use.
[0046] The frequencies of the random telegraph noise generated by
the magnetic fluctuations of the AFM crystal grains are smaller
when the magnetic anisotropic energy of the AFM crystal grains is
large, and may be controlled to have frequencies below about kHz
that do not affect the reading of the read signal by adjusting the
magnetic anisotropic energy of the crystal grains. Conversely, the
frequencies of the magnetic fluctuations of AFM crystal grains
become larger when the magnetic anisotropic energy of the AFM
crystal grains is small, and becomes random telegraph noise above
about 1 kHz that negatively affects the reading of the read signal
when the magnetic anisotropic energy of the crystal grains is less
than the specified value. Consequently, the read head structures
described herein according to various embodiments allow for the
magnetic anisotropic energy of the AFM crystal grains to be
proportional to the volume of the crystal grains.
[0047] To reduce the MnIr of the crystal nanograins, the seed layer
material is appropriately selected. In one approach, MnIr having an
L.sub.12 ordered alloy may be laminated to a thickness of at least
about 50 .ANG. on a multilayer seed film of Ru laminated on an
amorphous alloy film comprising Co, preferably as a major component
(equaling greater than about 50% of the material). Thus, of the
polycrystalline grains forming MnIr, a total volume of crystal
grains having a crystal grain volume of no more than about
1.2.times.10.sup.-19 cm.sup.3 may be less than about 3%, and
preferably about 1%, of the volume of the entire MnIr. The
amorphous alloy comprising Co may be a Co--X alloy, where X
includes at least one of the following, elements: Zr, Nb, Ta, Hf,
W, Si, and Al. Of course, other elements may be used.
[0048] In one approach, the structure of the read head may be
laminated MnIr layers having an L.sub.12 ordered alloy on a seed
film of a Ru film laminated on a Ta alloy film. Of the polycrystals
forming MnIr, the total volume of the crystal grains having a
crystal grain volume of 1.2.times.10.sup.-19 cm.sup.3 or smaller
may be no more than about 3%, and preferably about 1%, of the
volume of the entire MnIr. The Ta alloy film may be a Ta--X alloy,
where X includes at least one of Si and Al.
[0049] A read head according to another embodiment may be
manufactured using a manufacturing method that has a process that
deposits an amorphous alloy film comprising Co on a substrate,
deposits a Ru film above the amorphous alloy film, and forms MnIr
above the Ru film after heating the substrate to between about
150.degree. C. and about 300.degree. C., then cools the
substrate.
[0050] FIG. 1A shows a sensor 100 having a laminated structure. An
AFM layer 104 is formed above a seed layer 102. The AFM layer 104
may comprise MnIr and is strongly magnetically coupled by exchange
coupling with the ferromagnetic layer AP1 106 formed thereabove. A
ferromagnetic layer (AP2) 110 is strongly antiparallel coupled to
the ferromagnetic layer (AP1) 106 through a thin exchange layer 108
which may comprise Ru. AP1/exchange/AP2 is referred to as the
pinned layer 112. The magnetic moment of the pinned layer 112 is
strongly pinned by the AFM layer 104. An insulated barrier layer
114 which may comprise MgO, is positioned above the AP2 110, and a
ferromagnetic free layer (FL) 116 is positioned above the barrier
layer 114, then a cap layer 118 is positioned above the free layer
116. The free layer 116 responds to an external, magnetic field.
The direction of the magnetic moment of the free layer 116 is
changed by an external magnetic field.
[0051] The process for reading magnetic information recorded on a
recording medium using a tunneling magnetoresistive (TMR) sensor is
as follows. The direction of the magnetic moment of the free layer
116 is changed by the leaking magnetic field from the medium. When
the direction of the magnetic moment of the free layer 116 changes,
the sensor resistance changes and is detectable as a voltage
signal.
[0052] Now referring to FIG. 1B, the three sensor films A, B, and E
may be fabricated via sputtering. Sensor films A and B have a seed
layer of Ta 15 .ANG./Ru 20 .ANG., and sensor film E has a seed
layer of CoHf 40 .ANG./Ru 20 .ANG.. The Hf composition of CoHf is
23 at % and the layer has an amorphous structure. The composition
of MnIr is 22 at % Ir. In sensor film A, the substrate temperature
during MnIr deposition is room temperature. In sensor films B and
E, the substrate temperature is increased to 200.degree. C. and
deposition is performed at these temperatures.
[0053] FIG. 2A shows the MnIr structure of a face-centered cubic
(fcc) disordered phase MnIr and FIG. 2B shows the MnIr structure of
a L.sub.12 ordered phase. In the former, the Mn atoms 202 and Ir
atoms 204 randomly occupy the lattice positions in a fcc lattice.
As shown in FIG. 2A, there is no specific ordering of the atoms,
and thus they are all represented to appear the same. The
particular selection of which atoms are which is for exemplary
purposes only, and any random ordering could be produced. L.sub.12
ordered phase MnIr is an alloy having an atom arrangement with a
structure that places Mn atoms 202 in the center positions of the
faces of the fcc lattice and places Ir atoms 204 in the corner
positions.
[0054] The results of a detailed study of magnetic fluctuations in
the MnIr AFM layer forming each of the sensors A, B, E showed that
the fluctuations are caused by random telegraph noise in the low
frequency range of the playback head. The crystal properties and
temperature characteristics of MnIr are described below.
[0055] FIG. 3 shows the results of measuring the degree of order of
the L.sub.12 ordered phase MnIr. The results show that sensor film
A has a degree of order of zero for all MnIr film thicknesses and
becomes fcc disordered MnIr. Sensor films B and E have a degree of
order of an L.sub.12 ordered phase that increases with the MnIr
film thickness, and the degree of order at a 60 .ANG. film
thickness exhibits a value of approximately 0.2 to 0.3.
[0056] In addition, the MnIr crystal grain size of these sensors is
determined by observations using a transmission electron
microscope. FIG. 4 shows the results. Compared to sensor film A
that comprises deposited MnIr at room temperature, sensor film B
that used the same seed structure and hot film deposition has a
somewhat larger crystal grain size. In sensor film E that used a
different seed and hot film deposition, the crystal grains are
coarser. The average crystal grain size of sensor film A is 43
.ANG.; and the variance of the grain size is 14 .ANG.. The average
crystal grain size of sensor film B is 57 .ANG.; and the variance
of the grain size is 19 .ANG.. The average crystal grain size of
sensor film E is 72 .ANG.; and the variance of the grain size is 25
.ANG..
[0057] FIGS. 10A-10C show the temperature dependence of the
exchange coupling magnetic field Hp between the AFM layer and the
AP1 of each sensor (sensor film A in FIG. 10A, sensor film B in
FIG. 10B, and sensor film E in FIG. 10C) and the coercive force Hc.
Hp decreased with the temperature and became zero near 250.degree.
C. in sensor film A and near 350.degree. C. in sensor films B and
E. The temperature where Hp becomes zero is referred to as the
blocking temperature Tb. The coercive force Hc increases with the
temperature and becomes the maximum in the vicinity of the blocking
temperature Tb of each sensor, and then decreases. The behaviors of
the temperature dependence of Hc and Hp of the exchange coupling
film of the AFM layer and the ferromagnetic layer of a
polycrystalline structure are explained in more detail in K.
Nishioka et. al., "Grain size elect on ferro-antiferro coupling of
NiFe/FeMn systems," J. Appl. Phys., 80, 4528 (1996), and K.
Nishioka et. al., "Thickness effect on ferro-antiferro coupling of
Co/CrMnPt systems," J. Appl. Phys., 83, 3233 (1998).
[0058] The temperature changes of Hp and Hc calculated by using the
distribution of the crystal grain size obtained in FIG. 4 are
indicated by the solid line in FIGS. 10A-10C with the parameter of
the magnetocrystalline anisotropic constant of MnIr. The
calculation results are explained by empirical results, FIG. 5
shows the temperature changes of the crystal magnetic anisotropic
constant Ka of the MnIr obtained by calculations. In sensor films B
and F having a L.sub.12 ordered phase MnIr, a large
magnetocrystalline anisotropic constant Ka is exhibited compared to
sensor film A that does not have a L.sub.12 ordered phase MnIr. The
temperature where Ka is extinguished (Neel temperature) is near
400.degree. C. and has a higher value in sensor films B and E,
compared to the 300.degree. C. of sensor film A. The reason that a
large magnetocrystalline anisotropic constant Ka is exhibited in
sensor films B and E is that the MnIr becomes L.sub.12 ordered
alloy.
[0059] From these calculation results, the magnetic fluctuations of
the AFM MnIr crystal grains of each sensor film may be determined.
FIG. 6 is a graph of the percentage of MnIr crystals that fluctuate
at the frequencies of the magnetic fluctuations. For any test
sample, as the fluctuation frequency becomes smaller, the AFM
crystal grains increase. In other words, there are many AFM
crystals that have a low frequency and fluctuate slowly, and there
are few crystal grains fluctuating rapidly at high frequencies.
This frequency dependence is the so-called noise. When the measured
samples are compared, sensor films B and E that have L.sub.12
ordered phase MnIr have small noise components compared to sensor
film A that does not have L.sub.12 ordered phases. The reason for
large noise components in sensor film A compared to sensor films B
and E in all frequency regions is thermal instability because the
crystal grain sizes of MnIr are small and the magnetocrystalline
anisotropic constant Ka is small, and the magnetocrystalline
anisotropic energy represented by the product of the MnIr crystal
grain and Ka is small.
[0060] In addition, the reason sensor film E, that uses a Co
amorphous alloy in the seed layer, has a smaller noise component
than sensor film B, that uses a Ta seed layer, is the large
magnetocrystalline anisotropic energy because the crystal grain
size is large for sensor film E as shown in FIG. 4 compared to
sensor film B.
[0061] FIG. 7 is a graph of the results in FIG. 6 plotted as the
percentage of MnIr crystal grains having a relaxation time below
the relaxation time, .tau., of noise, which is the inverse of the
magnetic fluctuation frequency, with the horizontal axis being the
relaxation time. Each curve has a noise component that is nearly
zero at f=100 MHz (.tau.=1.times.10.sup.-8 seconds) and rapidly
increases from f=50 MHz (.tau.=5.times.10.sup.-8 seconds) and lower
frequencies. These characteristics are identical to the random
telegraph noise observed at the read head. Thus, magnetic
fluctuations of the AFM crystals are believed to be the cause of
the random telegraph noise.
[0062] In addition, the random telegraph noise that negatively
affects the interpretation of the read signal is the magnetic
fluctuations of the AFM crystals having frequencies mostly above 1
kHz. To guarantee stable performance of the read head, sensor film
E should be used. Thus, the percentage of AFM crystals having
frequencies above 1 kHz may be no more than about 3%, and
preferably 1%.
[0063] FIG. 8 shows the results for sensor film E of the
relationship between the MnIr crystal grain size and the relaxation
time .tau. of magnetic fluctuations where the film thicknesses of
MnIr were set to 40 .ANG., 50 .ANG., and 60 .ANG.. As the MnIr
becomes thick, .tau. becomes large. As the crystal grain size
becomes large, .tau. becomes large. The reason is that the
magnetocrystalline anisotropic energy of the crystal grains becomes
large as the film becomes thicker and the grain size increases. The
MnIr crystal grain size, Lc, at the critical boundary where the
relaxation time is .tau.=1 msec becomes larger as the MnIr
thickness becomes thinner, from 60 .ANG. to 50 .ANG. to 40 .ANG..
This is believed to occur because .tau. is determined by the volume
of the AFM crystal grains, and .tau. is not determined by the grain
size.
[0064] FIG. 9 is a graph of the relaxation time of noise where the
volume of the AFM crystal grains is the horizontal axis for sensor
films having different MnIr film thicknesses. The result is that
nearly the same straight line is found even for different MnIr film
thicknesses. Thus, the relaxation time of noise is determined by
the volume of the crystal grains when the magnetocrystalline
anisotropic constant is the same. For sensor films B and E, the
MnIr crystal grain volume Vc is 1.2.times.10.sup.-19 cm.sup.3 at
the critical region where the relaxation time is .tau.=1 msec.
[0065] Referring now to FIG. 11, there is shown a magnetic data
storage system, e.g., a disk drive 1100, in accordance with one
embodiment of the present invention. As shown in FIG. 11, at least
one magnetic storage medium, e.g., a rotatable magnetic disk 1112,
is supported on a spindle 1114 and rotated by a drive mechanism,
which may include a disk drive motor 1118. The magnetic recording
on each disk is typically in the form of an annular pattern of
concentric data tracks (not shown) on the disk 1112.
[0066] At least one slider 1113 is positioned near the disk 1112,
each slider 1113 supporting one or more magnetic read/write heads
1121. As the disk rotates, slider 1113 is moved radially in and out
over disk surface 1122 so that heads 1121 may access different
tracks of the disk where desired data are recorded and/or to be
written. Each slider 1113 is attached to an actuator arm 1119 by
means of a suspension 1115. The suspension 1115 provides a slight
spring force which biases slider 1113 against the disk surface
1122. Each actuator area 1119 is attached to an actuator 1127. The
actuator 1127 as shown in FIG. 11 may be a voice coil motor (VCM).
The VCM comprises a coil movable within a fixed magnetic field, the
direction and speed of the coil movements being controlled by the
motor current signals supplied by controller 1129.
[0067] During operation of the disk storage system, the rotation of
disk 1112 generates an air bearing between slider 1113 and disk
surface 1122 which exerts an upward force or lift on the slider.
The air bearing thus counter-balances the slight spring force of
suspension 1115 and supports slider 1113 off and slightly above the
disk surface by a small, substantially constant spacing during
normal operation. Note that in some embodiments, the slider 1113
may slide along the disk surface 1122.
[0068] The various components of the disk storage system are
controlled in operation by control signals generated by controller
1129, such as access control signals and internal clock signals.
Typically, controller 1129 comprises logic control circuits,
storage e.g., memory), and a microprocessor. The controller 1129
generates control signals to control various system operations such
as drive motor control signals on line 1123 and head position and
seek control signals on line 1128. The control signals on line 1128
provide the desired current profiles to optimally move and position
slider 1113 to the desired data track on disk 1112. Read and write
signals are communicated to and from read/write heads 1121 by way
of recording channel 1125.
[0069] The above description of a typical magnetic disk storage
system, and the accompanying illustration of FIG. 11 is for
representation purposes only. It should be apparent that disk
storage systems may contain a large number of disks and actuators,
and each actuator may support a number of sliders.
[0070] An interface may also be provided for communication between
the disk drive and a host (integral or external) to send and
receive the data and for controlling the operation of the disk
drive and communicating the status of the disk drive to the host,
all as will be understood those of skill in the art.
[0071] In another embodiment, a method 1200 forming a magnetic read
head is shown according to one embodiment. As an option, the
present method 1200 may be implemented to construct structures such
as those shown in FIG. 1A. Of course, however, this method 1200 and
others presented herein may be used to form magnetic structures for
a wide variety of devices and/or purposes which may or may not be
related to magnetic recording. Further, the methods presented
herein may be carried out in any desired environment. It should
also be noted that any aforementioned features may be used in any
of the embodiments described in accordance with the various
methods.
[0072] In operation 1202, a seed layer is formed above a substrate,
such as via sputtering, plating, vapor deposition, or any other
known technique in the art. The seed layer may comprise an
amorphous alloy film of Co--X alloy. The Co--X alloy comprises more
Co (Co is a major component) than any other element, with X being
selected from a group which includes at least one of: Zr, Nb, Ta,
Hf, W, Si, and Al, that is, X may be more than one element in the
group. In a further approach, the seed layer may further comprise a
Ru film positioned above the Co--X alloy film.
[0073] In operation 1204, at least the substrate is heated (the
seed layer may also be heated) to a first temperature in a range
from about 150.degree. C. to about 300.degree. C. The heating may
be accomplished using any technique known in the art, such as
passing heated air across the substrate, holding the substrate in
an environment having an elevated temperature, such as an oven,
etc.
[0074] In operation 1206, an AFM layer is formed above the seed
layer after the heating 1204, such as between the heating 1204 and
the cooling 1208, the AFM layer comprising a MnIr alloy. Any method
of forming may be used as would be understood by one of skill in
the art.
[0075] In operation 1208, at least the substrate is cooled (the
seed layer may also be cooled) to a second temperature of less than
about 100.degree. C. Any technique for cooling the substrate may be
used, such as waiting while the substrate is in a lower temperature
environment, passing cooler air over the substrate, etc.
[0076] The method 1200 may further include forming a first
ferromagnetic layer (AP1) above the AFM layer, forming an exchange
layer above the first ferromagnetic layer, forming a second
ferromagnetic layer (AP2) above the exchange layer (the first
ferromagnetic layer, the exchange layer, and the second
ferromagnetic layer forming a pinned layer), forming a barrier
layer above the pinned layer, and forming a ferromagnetic free
layer above the barrier layer. The ferromagnetic free layer is
adapted to respond to an external magnetic, field, a magnetic
moment of the pinned layer is strongly pinned by the AFM layer, the
AFM layer is strongly magnetically coupled by exchange coupling
with the first ferromagnetic layer, the second ferromagnetic layer
is strongly antiparallel coupled by the AFM layer, and the barrier
layer comprises MgO.
[0077] In a further approach, the MnIr alloy may have an L.sub.12
ordered phase, and a percentage of a volume of MnIr crystal grains
in the MnIr alloy having a magnetic relaxation tune of about 1 msec
or less with respect to a total volume of MnIr may be less than
about 3% (and less than about 1% in some approaches) at a maximum
temperature of the magnetic read head during operation.
[0078] In another further approach, the MnIr alloy may have an
L.sub.12 ordered phase, and less than about 3% (and less than about
1% in some approaches) of polycrystalline grains forming the AFM
layer have a crystal grain volume of about 1.2.times.10.sup.-19
cm.sup.3 or less.
[0079] While various embodiments have been described above, it
should be understood that they have been presented by way of
example only, and not limitation. Thus, the breadth and scope of an
embodiment of the present invention should not be limited by any of
the above-described exemplary embodiments, but should be defined
only in accordance with the following claims and their
equivalents.
* * * * *